1. Technical Field
The present disclosure relates to a digital hologram display device displaying 3D image by using a spatial light modulator.
2. Discussion of the Prior Art
Nowadays researches for three dimension (3D) image and implementing the 3D image are done actively. A 3D image technique provides 3D image corresponding to a full real appearance of an object for observer while a two dimensional (2D) image technique provides image corresponding to a plane view of an object. Thus, the technology of implementing 3D image is an ultimate technology.
Typically three methods are known for reproducing 3D image; a stereoscopic method, a holographic method, and an integral imaging method. The holographic method uses laser beam so that it is possible to observe the 3D image with naked eyes. The holographic method is the most ideal method because and it has an excellent visual stereoscopic property and observer watches the 3D image without any fatigue.
The holographic method records optical interference obtained from superposition of an object beam and a reference beam on a film. The object beam refers to a beam distracted from an object by illuminating a laser beam which has a high coherency, and the reference beam refers to a beam having a high coherency. More specifically, the optical interference can be a series of interference fringes including intensity information and phase information of a light wave, and the film can be a standard photographic film. Thus, the interference fringes are recorded on the standard photographic film. The interference fringes form a type of diffraction grating on the film, which is called the hologram. Therefore, the holographic method can reproduce the 3D image by illuminating the reference beam to the interference fringes.
There was a new development of the computer generated holography (CGH) that is the method of digitally generating the interference fringes. For example, a holographic interference pattern can be generated by digitally computing the interference fringes and printing it onto a mask or film for subsequent illumination by suitable coherent light source. Recently, the computer generated holography for displaying a dynamic image as well as a static image is developed.
The computer generated holography transmits holographic interference pattern data to a spatial light modulator (in the below, referred to as SLM) such as LCSLM (Liquid Crystal Spatial Light Modulator). Then, the SLM displays the holographic interference pattern and the holographic interference pattern is reproduced to the 3D image by illuminating the reference beam to the SLM.
FIG. 1 is the structural drawing illustrating a digital hologram display device using a computer generated holography according to the prior art. Referring to FIG. 1, a computer 10 generates the holographic interference pattern data to be displayed on the SLM 20 and transmits the holographic interference pattern data to the SLM 20. The SLM 20 can be implemented as the LCSLM. In this case, the SLM 20 can be a transmittive liquid crystal display device. The SLM 20 can represent the holographic interference pattern. At one side of the SLM 20, a laser source 30 for generating the reference beam is located. In order to radiate the reference beam 90 from the laser source 30 onto the whole surface of the SLM 20, an expander 40 and a lens system 50 can be disposed, sequentially. The reference beam 90 out from the laser source 30 is radiated to one side of the SLM 20 passing through the expander 40 and the lens system 50. As the SLM 20 is a transmittive liquid crystal display device, the holographic interference pattern will be reproduced at the other side of the SLM 20.
U.S. Pat. No. 5,416,618 discloses a 3D image display device of the holographic method using two transmittive liquid crystal displays. More specifically, U.S. Pat. No. 5,416,618 uses a first SLM for modulating phase of light and a second SLM for modulating amplitude of light in order to maximize an interference of light. Therefore, U.S. Pat. No. 5,416,618 implements the 3D image as a hologram by the interference of light. However, U.S. Pat. No. 5,416,618 has four disadvantages as following: (1) it is difficult to align the first SLM with the second SLM, (2) cost for fabricating the 3D image display device is increased due to two SLMs, (3) thickness of 3D image display device is thicker, and (4) driving of the 3D image display device is complex.